Wheatstone bridge testing arrangement



o ct. 6, 1953 R. M. M oBERMAN ETAL 2,654,837

WHEATSTONE BRIDGE TESTING ARRANGEMENT Filed May 5, 1948 @YMLMQ Patented ct. 6, 19.53

OFFICE WHEATSTONE BRIDGE TESTING ARRAN GEMEN T Roelof M. M. Oberman and Antonie Snijders, The Hague, Netherlands Application May 5, 1948, Serial No. 25,108 In the Netherlands May 8, 1947 s claims. 1

The invention relates to an arrangement for testing Wheatstone direct current bridges as e. g. required in transmission systems, in which selectors are positioned through the application of this principle.

In a known arrangement of this kind four tubes are provided and it is therefore an expensive element in the controlling register of the mentioned kind of transmission systems.

Though the arrangement according to the lnvention contains only two tubes, it has the same elect as the known one, cost and space being economized. In one embodiment of the present invention an input tube has two electrodes, the voltages of which change in opposite sense under the control of the control grid are each connected on one side via a resistor to one terminal of a voltage source (VH-V2) and on the other side via a voltage divider to the other terminals of the voltage source (VH-V2) while the tapping points of the two voltage dividers are connected via two rectiers (which are arranged in the same sense) to a control electrode (e. g. the control grid) of an output tube, another controlling electrode (e. g. the cathode) of which is connected to a tapping of the voltage source so that, when the input voltage changes from one value to another, the conductivity of the output tube is first reversed under the control of one of the voltage dividers, while under the control of the other voltage divider the output tube resumes its original condition after the conductivity of the mentioned rectiers has been reversed.

The invention will be explained more in detail with reference to the drawings in which:

Fig. 1 is a wiring diagram of an embodiment of the present invention.

Figs. 1a and 1b are diagrams for explaining the operation of the arrangement according to Fig. l and Fig. 2 shows a modication of the arrangement according to Fig. 1.

The arrangement according to Fig. 1 shows a zero indicator, termed zero switch hereafter, having two conventional high vacuum tubes, such as pentodes B1 and B2. The input terminals A and B, which are inserted in the galvanometer branch of a Wheatstone bridge (not shown), are connected to the input tube B1 (termed here-` inafter the first tube) via rectifying means G1 and resistive means R1, optionally with the insertion of a source (not shown) of low voltage for the positioning of the grid Voltage-anode current characteristic of the tube B1.

The rectiiier G1 and the resistor R1 protect the input tube B1 against input voltages which make terminal A positive with respect to terminal B, because the rectier G1 is conductive for input voltages which make terminal A negative with respect to terminal B, so that the control grid voltage of the input tube B1 can follow the applied voltage, whereas the rectifier G1 is nonconductive for input voltages of opposite polarity. The anode of tube B1 is connected to a resistor R2 and the cathode to a resistor Rc. The junction of the anode of the input tube and the resistor R5 is connected via a voltage divider consisting of the resistors R4 an-d R5 to the negative terminal of the total voltage source (VH-V2) whereas the function of the cathode of the input tube B1 and the resistor RSM connected to the positive terminal of the voltage source (V1, V2) via a voltage divider consisting of the resistors Re and R7.

The tapping points X and Y of the two voltage dividers are connected to the control grid of the output tube B2 (termed hereinafter the second tube), via the rectiers G2 and G3, respectively.

When the input tube B1 is non-conductive owing to a suiiiciently high negative input voltage, the potentials of the points X and Y are determined by the ratio of the component resistors of the voltage ydividers which have large resistance values in comparison to the resistors R2 and Ra.

When the potential of the point X is positive and the potential of the point Y negative with respect to the cathode of the output tube B2 and the input tube B1 becomes conductive, the potential of the point X becomes negative and the potential of the point Y becomes positive with respect to that of the cathode of the output tube B2, the anode of the input tube B1 becoming less positive and the cathode of this tube becoming less negative. The tapping points of the two voltage dividers represent this change in the ratio of their component resistors.

The two rectiers G2 and G3 form a connection between the points X and Y. Dependent on the polarity of the voltage difference between these two points one rectifier will be conductive and the other one non-conductive.

When the input tube B1 under the influence of a suiciently high negative input voltage is nonconductive, the output tube B2 is also non-conductive under the influence of the potential of the point Y which is transferred to the grid of tube B2 via the conductive rectifier Gc.

By a decrease of the negative input voltage the input tube B1 will become gradually conductive,

so that the voltage applied to the voltage divider Rs/Rv is decreased and the potential of the point Y becomes less negative so that the output tube B2 becomes quickly conductive. Thus the output tube follows the change in potential of the point Y. When the potential difference of the points X and Y changes thesize thereof in consequence of the input voltage changing less negative values, the rectier G2 becomes conductive, the rectifier Gs becoming non-conductive so that the output tube follows the potential change of the ,point .X. At a further change of the input voltage to even lesser negative values the point X assumes a negative potential with respect totheY cathode of the output tube B2, so that the latter is brought again into non-conductive condition under the control of the potential of the point X, via the conductive rectiiier G2. The anode current characteristics of the two tubes B1 and B2 are'shown diagrammatically in Fig. la. Fig. la illustrates the anode current characteristic curves of tubes fBi and B2 vs. input voltage. It will be notedfrom Fig. la that the change inanode current in tube B1 is substantially linear `whilethe plate current variation of tube B2 assumes a lsubstantially rectangular form. The slope of theleadingA andthe lagging edges ofthe current curve of tube B2 may be controlled by properl choice of the resistors R4, Rs, and Re, R7 of the two voltage dividers. It is therefore possible to adjust the rise time and the decay time of the current curve of tube B2 to any suitable value, preferably-approaching as closely as possible, zero rise and decay time.

It is also possible to-reverse the two rectiers G2 and Gs in the circuit so that when tube B1 has no anode current flowingtherethrough (as a result of a large negative input potential) tube B2 will conduct maximum platecurrent as indicated in Fig. lb. When the rectiers G2 and G3 are connected in reverse direction-to the direction illustrated in the circuit of Fig. 1, `a different cathode potential must be suppliedA to the cathode of tube B2 than the cathode potential used in the arrangement-illustrated in Fig. 1. As the input potential becomes less negative, anodecurrent will begin to flow-in tube B1 as-indicated in Fig. 1b, whereas plate current flow through tube Bz will decrease rapidly until :plate current flow through tube B2 is completely cut off. This occurs when the polarity of the potential difference between X and Y is reversed, therebyimaking'the rectifier G2 conductive. and the rectifier G2 nonconductive. As the input voltage becomes even less negative, output'tube-Bz will follow the'potentialof the point Y which will change from a negative to a positive value with'respect to the potential of the. cathode of tube B2. At that point the outputtube B2 again becomes conductive as indicated in Fig. 1b.

The advantage of the characteristic according to Fig. 1b is'the following. When the zero indicator is used in transmission-systems in which selectors are positioned by meansvof theequilibrium of Wheatstone direct current bridges, use is made of the release'time of a testing device'or relay T connected in the vanode circuit of the output tube. As a rule a device is obtained that functions much Vmore quickly with a smaller capacity of the output vtube than .a device in which the test relay attracts'the armature when the selector to be'positicned iinjds bridge equilibrium.

Fig. 2 shows a modified embodiment of the arrangement according to Fig. 1. A drawback ci the `arrangement according to Fig. 1 is that the anode voltage sources V1 and V2 cannot serve for more than one joint zero switch, which drawback has been overcome by the embodiment shown in Fig. 2 by the use of an input tube B1 with a secondary emission electrode. Otherwise, the arrangement, which, as regards the application of .a secondary emission electrode only shown inprinciple in Fig-2, is equalto the arrangement according to Fig. l.

'The characteristics that are to be obtained, correspond to those shown in Figs. 1a and 1b.

Without further explanation it will be clear that one-sided characteristics of the zero switch can be obtained by disconnecting one of the points X or Y from the rectifiers G2 or Gc, i. e. characteristics in which the output tube at a certain input Voltage changes its conductive condition, These characteristics are e. g. required inV transmission systemswhen a voltage that is greater or smaller than a certain value, has to be found.

vWhile wehave illustrated and described what weregard to be thepreferred embodiment of our invention, nevertheless it Awilli be .understoodithat such is merely exemplary and Ithat .numerous modiiications and rearrangements mayjbeimade therein without departing from the essence of the invention.

W e claim:

l. A testing arrangementfor insertionintothe.

galvanometer branch of .a W-heatstone v.13. iC. bridge arrangement, comprising, :in combination. a rst vacuum tube having a "cathodefavcontrol grid, and an anode; an input ,circuit including said cathode and said .control grid of Saidzziirst tube and being inserted 'into the ygalvanonfieter branch ci the Wheatstone D. 1C. bridge arrangement so .as :to :be `irrxparted Va di-rect voltage depending as uto sign and magnitude on the condition of'the WheatstoneD. C. bridge arrangement; a voltage .-source having'a `.ta-pir-1' and a positive and a negative terminal, said negative terminal being connected tosaid cathode of said iirst tube, said positive terminal being connected to said anode of said rst tube; arst voltage divider having a tapping and being in serted between said anode of nsaidlrst `tubeand said negative terminal of saidvoltagesource; a second voltage f divider having a teppingand being inserted between said ucathode Of said -irst tube and said positive .terminal-Qi said voltage source, whereby said tappings of `said Avoltage div-idersuare imparteda potential difference'depending on the sign and magnitude of thefdirect voltage imparted to said inputci-rcuityafseccnd vacuum tube having a catho.de,-a control grid and an anode, said ,cathode of said .second tube being connected to said ltapping-ofsaidvoltage source; a first rectier'and*a-second-rectiier-inserted, respectively, between saidccntrol grid-,of said second tube and said tappings of said voltage dividers so that one of said .rectiiers is -con ductive and the other non-conductivedepending on the sign ofthe-potential difference .imparted to said tappings of `said voltage dividers; .anda testing device inserted betweenthe Aanode of.A said second tube andsaid positiveterminal-.of `said voltage source, whereby the anode hcurrent of said second tube .flowing through said testing device is responsive lto the potentialdifference imparted yto said tappings of said voltage `dividers, vwhich .in turndependson thesign and magnitude of the direct voltage imparted to said input circuit.

2. A testing arrangement for insertion vinto the galvanometer'branchcof a Wheatstone D. C. bridge arrangement, comprising,einfcombination,

a first vacuum tube having a cathode, a control grid, and an anode; an input circuit including said cathode and said control grid of said first tube and being inserted into the galvanometer branch of the Wheatstone D. C. bridge arrangement so as to be imparted a direct voltage depending as to sign and magnitude on the condition of the Wheatstone D. C. bridge arrangement; a voltage source having a tapping and a positive and a negative terminal, said negative terminal being connected to said cathode of said iirst tube, said positive terminal being connected to said anode of said first tube; a first voltage divider having a tapping and being inserted between said anode of said first tube and said negative terminal of said voltage source; a second voltage divider having a tapping and being inserted between said cathode of said iirst tube and said positive terminal of said voltage source, whereby said tappings of said voltage dividers are imparted a potential difference depending on the sign and magnitude of the direct voltage imparted to said input circuit; a second vacuum tube having a cathode, a control grid and an anode, said cathode of said second tube being connected to said tapping of said voltage source, said voltage dividers being so dimensioned that one of said tappings of said voltage dividers is positive and the other of said tappings of said voltage dividers is negative with respect to said i cathode of said second tube; a first rectiiier and a second rectifier inserted, respectively, between said control grid of said second tube and said tappings of said voltage dividers so that one of said rectiers is conductive and the other nonconductive depending on the sign of the potential difference imparted to said tappings of said voltage dividers; and a testing device inserted between the anode of said second tube and said positive terminal of said voltage source, whereby the anode current of said second tube owing through said testing device is responsive to the potential difference imparted to said tappings of said voltage dividers, which in turn depends on the sign and magnitude of the direct voltage imparted to said input circuit.

3. A testing arrangement for insertion into the galvanometer branch of a Wheatstone D. C. bridge arrangement, comprising, in combination, a i'irst vacuum tube having a cathode, a control grid, and an anode; an input circuit including said cathode and said control grid of said rst tube and being inserted into the galvanometer branch of the Wheatstone D. C. bridge arrangement so as to be imparted a direct voltage de pending as to sign and magnitude on the condition of the Wheatstone D. C. bridge arrangement; rectifying means inserted between said control grid of said rst tube and one of the terminals of the galvanometer branch of the Wheatstone D. C. bridge arrangement, said rectifying means allowing current to pass only when said one terminal of the galvanometer branch has a lower potential than the other terminal of the galvanometer branch; a voltage source having a tapping and a positive and a negative terminal, said negative terminal being connected to said cathode of said rst tube, said positive terminal being connected to said anode of said irst tube; a first voltage divider having a tapping and being inserted between said anode of said rst tube and said negative terminal of said voltage source; a second voltage divider having a tapping and being inserted between said cath ode of said rst tube and said positive terminal of said voltage source, whereby saidtappings of said voltage dividers are imparted a potential difference depending on the sign and magnitude of the direct voltage imparted to said input circuit; a second vacuum tube having a cathode, a control grid and an anode, said cathode of said second tube being connected to said tapping of said voltage source; a rst rectier and a second rectifier inserted, respectively between said control grid of said second tube and said tappings of said voltage dividers so that said rectilers are conductive and the other non-conductive depending on the sign of the potential diierence imparted to said tappings of said voltage dividers; and a testing device inserted between the anode of said second tube and said positive terminal of said voltage source, whereby the anode current of said second tube iiowing through said testing device is responsive to the potential difference imparted to said tappings of said voltage dividers, which in turn depends on the sign and magnitude of the direct voltage imparted to said input circuit.

4. A testing arrangement for insertion into the galvanometer branch of a Wheatstone D. C. bridge arrangement, comprising, in combination, a rst vacuum tube having a cathode, a control grid, and an anode; an input circuit including said cathode and said control grid of said first tube and being inserted into the galvanometer branch of the Wheatstone D. C. bridge arrangement so as to be imparted a. direct voltage depending to and magnitude on the condi tion of the lli/heatstone D. C. bridge arrangement; rectifying means inserted between said control grid of said first tube and one of the terminais or the galvanometer branch of the Wheatstone D. C. bridge arrangement, said rectifying means allowing current to pass only when one terminal of the galvanometer branch a lower potential than the other terminal of the galvanometer branch; resistive means inserted between said cathode of said first tube and the junction of said rectifying means and said grid of said rst tube; a voltage source having a tapping and a positive and a negative terminal, said negative terminal being connected to said cathode of said iirst tube, said positive terminal being connected to said anode of said first tube; a drst voltage divider having a tapping and being inserted between said anode of said iirst tube and said negative terminal of said voltage source; a second voltage divider having a tapping and being inserted between said cathode of said iirst tube and said positive terminai of said voltage source, whereby said tappings of said voltage dividers are imparted a potential difference depending on the sign and magnitude oi the direct voltage imparted to said input circuit; a second vacuum tube having a cathode, a control grid and an anode, said cathode ci said second tube being connected to said tapping of said Voltage source; a first rectiiier and a second rectifier inserted, respectively, between said control grid of said second tube and said tappings of said voltage dividers so that said rectiiiers are conductive and the other non-conductive depending on the sign of the potential diilierence imparted to said tappings of said voltage dividers; a testing de vice inserted between the anode of said second tube and said positive terminal of said voltage source7 whereby the anode current of said second tube iiowing through said testing device is responsive to the potential difference imparted to said tappings of said voltage dividers, which in turn depends on the sign and magnitude of the direct voltage imparted to said `input circuit.

5. A testing arrangement for insertion into the galvanometer branch of a Wheatstone D. C. bridge arrangement, comprising, in combination, a nrst vacuum tube having a cathode, a control grid, and an anode; an input circuit including said cathode and said control grid of said rst tube and being inserted into the galvanometer branch of the Wheatstone D. C. bridge arrangement so as to be imparted a direct voltage depending as to sign magnitude on the condition of the Wheatstone D. C. bridge arrangement; rectifying means inserted between said control grid of said rst tube and one of the terminals of the galvanometer branch of the Wheatstone D. C. bridge arrangement, said rectifying means allowing current to pass only when said one terminal of the galvanometer branch has a lower potential than the other terminal of the galvanometer branch; a voltage source having a tapping and a positive and a `negative terminal, said negative terminal being connected to said cathode of said first tube, said positive terminal being connected to said anode of said first tube; a first voltage divider having a tapping and being inserted between said anode of said first tube and said negative terminal of said voltage source; a second voltage divider having a tapping and being inserted between said cathode of said first tube and said positive terminal of said voltage source, whereby said tappings of said voltage dividers are imparted a potential difference depending on the sign and magnitude of the direct voltage imparted to said input circuit; a second vacuum tube having a cathode, a control grid and an anode, said cathode of said second tube being connected to said tapping of said voltage source; a rst rectifier and a second rectiiier inserted, respectively, between said control grid of rsaid second tube and said tappings of said voltage dividers so that oneo said rectiiers is conductive and the other non-conductive depending on the sign of the potential difference imparted to said tappings or said voltage dividers; and a testing device inserted between the anode of said second tube and said positive terminal of said voltage source, whereby the anode current of said second tube flowing through said testing device is responsive to the potential difference imparted to said tappings of said voltage dividers, which in turn depends on the sign and magnitude of the direct voltage imparted to said input circuit.

6. A testing arrangement for insertion into the galvanometer branch of a Wheatstone D. C. bridge arrangement, comprising, in combination, a rst vacuum tube having a cathode, a control grid, and an anode; an input circuit including said cathode and said control grid of said first tube and being inserted into the galvanometer branch of the Wheatstone D. C. bridge arrangement so as to be imparted a direct voltage depending as to sign and magnitude on the condition of the Wheatstone D. C. bridge arrangement; rectifying means inserted between said control grid of said first tube and one of the terminals of the galvanometer branch of the Wheatstone D. C. bridge arrangement, said rectifying means allowing current to pass only when said one terminal of the galvanometer branch has a lower potential than the other terminal of the galvanometer branch; resistive means inserted between said cathode of said first tube and the junction of said rectifying means and said grid of said rst tube; a voltage source having a tapping and a positive-and a negative terminal, said negative terminal being connected to said cathode of said rst tube, said positive terminal being connected to said anode of said first tube; a rst voltagedivider having a tapping and being Ainserted between said anode of said rst tube and said negative terminal of said voltage source; a second voltage divider having a tapping and being inserted between said cathode of said rst tube and said positive terminal of said voltage source, whereby said tappings of said voltage dividers are imparted a potential difference depending on the sign and magnitude of the direct voltage imparted to said input circuit; a second vacuum tube having a cathode, a control grid and an anode, said cathode of said second tube being connected to said tapping of said voltage source; a rst rectifier and a second `rectifier inserted, respectively, between said control grid of said second tube and said tappings of said voltage dividers so that one of said rectiiiers lis conductive and the other non-conductive depending on the sign of the potential diierence imparted to said tappings of said voltage dividers; and a testing device inserted between the anode of said second tube and said positive terminal of vsaid voltage source, whereby the anode current of said second tube owing through said testing device is responsive to the potential difference imparted to said tappings of said voltage dividers, which in turn depends on the sign and magnitude of the direct voltage imparted'to said input circuit.

7. A testing arrangement for 'insertion into the galvanometer branch of va Wheatstone D. C'. bridgearrangement, comprising, in combination,

a first vacuum tube having a cathode, a control grid, and an anode; an input circuit including said cathode and said control grid of said rst tube and being Vinserted into the lgalvanorneter branch of the Wheatstone D. C. bridge arrange ment so as to be imparted a direct voltage der pending as to sign and magnitude on the condition of the Wheatstone D. C. bridge arrangement; rectifying means inserted between said control'grid of said rst tube and one of the terminals of the galvanometer branch of the Wheatstone D. C. lbridge arrangement, saidsrectirying means vallowing current to pass .only when said one terminal of the galvanometer branch.

has a lower potential than the other terminal of the galvanometer branch; a voltage source having a tapping and a positive and a negative ter` minal, said negative terminal being connected to said cathodeof said rst tube, said positivej terminal being connected to said anode of said rst tube; a rst voltage divider having a tap' ping and being inserted between said anode of said rst tube and said negative terminal of said voltage source; Va second voltage divider having a tapping and being inserted between said-cathode of said first tube and said positive terminal of said -voltage source, whereby Vsaid tappings of said voltage dividers are imparted a potential diierence depending on the sign and mag-g4 nitude of the direct voltage imparted to said input circuit; a second vacuum tube having a cathode, a control grid and an anode, said cathode or said second tube being connected to said tapping of said voltage source, said voltage dividers being so dimensioned that one of said tappings of said voltage dividers is positive and the other of said tappings of said voltage dividers is negative with respect to said cathode 0f potential diierence imparted to said tappings of said voltage dividers, which in turn depends on the sign and magnitude of the direct voltage imparted to said input circuit.

8. A testing arrangement for insertion into the galvanometer branch of a Wheatstone D. C. bridge arrangement, comprising, in combination, a iirst vacuum tube having a cathode, a control grid, and an anode; an input circuit including said cathode and said control grid of said rst tube and being inserted into the galvanometer branch of the Wheatstone D. C. bridge arrangement so as to be imparted a direct voltage depending as to sign and magnitude on the condition of the Wheatstone D. C. bridge arrangement; rectifying means inserted between said control grid of said first tube and one of the terminals of the galvanometer branch of the Wheatstone D. C. bridge arrangement, said rectifying means allowing current to pass only when said one terminal of the galvanometer branch has a lower potential than the other terminal of the galvanometer branch; resistive means inserted between said cathode of said rst tube and the junction of said rectifying means and said grid of said first tube; a voltage source having a tapping and a positive and a negative terminal, said negative terminal being connected to said cathode of said rst tube, said positive terminal being connected to said anode of said iirst tube; a rst voltage divider having a tapping and being inserted between said anode of said first tube and said negative terminal of said voltage source; a second voltage divider having a tapping and being 10 inserted between said cathode of said first tube and said positive terminal of said Voltage source, whereby said tappings of said voltage dividers are imparted a potential difference depending on the sign and magnitude of the direct voltage imparted to said input circuit; a second vacuum tube having a cathode, a control grid and an anode, said cathode of said second tube being connected to said tapping of said voltage source, said voltage dividers being so dimensioned that one of said tappings of said voltage dividers is positive and the other of said tappings of said voltage dividers is negative with respect to said cathode of said second tube; a rst rectifier and a second rectier inserted, respectively, between said control grid of said second tube and said tappings of said voltage dividers so that one of said rectiers is conductive and the other non-conductive depending on the sign of the potential difference imparted to said tappings of said voltage dividers; and a testing device inserted between the anode of said second tube and said positive terminal of said voltage source, whereby the anode current of said second tube flowing through said testing device is responsive to the potential difference imparted to said tappings of said voltage dividers, which in turn depends on the sign and magnitude of the direct voltage imparted to said input circuit.

ROELOF M. M. OBERMAN. ANTONIE SNIJDERS.

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